desperate search for a california family missing for three days since their small plane went down in the idaho wilderness. The father, a silicon valley executive was piloting the plane when it disappeared. And abc's clayton sandell has the story. Reporter: This morning, search teams will be honing in on an emergency beacon that sounds like this. The signal, coming from somewhere in the rugged mountains 50 miles northeast of cascade, idaho. They have it narrowed around two to four-mile radius, where the aircraft might be. Reporter: After celebrating thanksgiving in san jose, california, dale smith was flying his son daniel, and daniel's wife, home sunday to butte, montana. The last leg of their trip started in baker city, oregon, and was supposed to take them over the continental divide. But at yellow pine, idaho, smith radioed he was having trouble. The beech bonanza never made it. Both are students at byu. He had come to thanksgiving dinner to meet her family. They are deeply in love. I got my wedding announcement a couple days ago. But they're scheduled to be MARRIED ON JANUARY 4th. Reporter: Smith is the ceo of a silicon valley tech firm. Family members say he's an expert pilot. All of the words I've heard to describe dale smith are the kind of words you would want to describe a pilot of a small aircraft. Competent. Conservati conservative. Meticulous. Reporter: Now, they're hoping for a miracle. The number one concern we have is that they have survived the crash and they may be injured. But they're having to survive in 10-degree weather at nighttime, possibly with snow coming down. And no way to keep warm. Reporter: Right now, the emergency beacon is coming in very weak, which makes it hard to locate. But rescuers will be back at it from the ground and the air at first light. Robin? They're working hard to find them. Clayton, thank you.

This transcript has been automatically generated and may not be 100% accurate.

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